This is the ValueSet that contains all the codes in Drug tier of medication in health plan (http://hl7.org/fhir/us/davinci-drug-formulary/ValueSet/DrugTierVS) and Drug tier of medication in health plan (http://hl7.org/fhir/us/davinci-drug-formulary/ValueSet/DrugTierVS). E.g. what you have to deal with if you get resources containing codes in either of them